Bleaching wood pulp



2Q, 1949 P. B. KBURG El AL 2,492,047

BLEACHING woon PULP Filed March 30, 1946 PA UL B. KBURG JOSEPH 's. REIGHERT IN V EN TOR.

A TTOR NE) Patented Dec. 20, 1949 UNITED snares PATENT OFFICE BLEACHING WOOD PULP Paul B. KBurg and Joseph S. Reichert, Niagara Falls, N. Y., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application March 30,

vantageous to remove a lar e part of the water 7 from the wood pul before subject ng it to bleaching o erat ons. In conventional high consistency bleaching operations. wood pulp of about 8 to consistency is mixed w th a bleaching chemical. for exam le, a peroxide solution. In such mixing operations. the pulp is a rather pasty mass and considerable time and power are required to obtain complete and un form mixing of the bleaching chemical with the pulp. In such o erations. care must be exercised to avoid localizing of bleaching and to obtain a uniform mixture of the pulp and the bleaching solution.

An object of the present invention is to provide a. new and improved process for bleaching wood pulps. peroxide bleaching solution to a high consistency wood pulp so as to obtain uniform action. of the bleaching solution on the wood pulp in a shorter time of operationthan is possible in-previously known methods. Further obiects will be apparent from the following description of the invention.

The above-mentioned objects are accomplished in accordance with the present invention by forming a mist-like d spersion of an auueous hydrogen peroxide solution in a, gas, such as air, and bringing high consistency wood pulp of at least 30% consistency (i. e.,-containing not more than 70% by weight of water) into contact with said dispersion. v

The appended drawing, which is an elevation partly in section, illustrates one form of apnara tus that may be used to practice the invention. A conventional screw conveyor mechanism 2 powered by'conventional motor and gear train 8, is adapted to feed granular material into arotating. hollow cylinder which. is rotated and supported by. conventional means: not shown.-

Hopper l is mounted to feed granular materialwood pulps,

A further object is the application of a 1946, Serial No. 658,585

(Cl. s 1o4) divided mist-like dispersion in air of liquid forced into pipe 5.

In a preferred method of practicing the invention. the process starts with freshly prepared wood .pulp, for example, groundwood which has a relatively low consistency. e. g., 0.5 to 6% consistency. This low consistency pulp is dewatered to form high consistency pulp of at least 30% consistency which may be obtained as individual fibers or small agglomerates. A convenient method for preparing such high consistency pulps is to utilize a pulp press such as is commonly utilized for dewatering vegetable by-products, such as tomato pomace and the like. An example of such a pulp press is one which consists essentially of a vertical perforated cylinder within which rotates a hollow perforated ele- 1 ment having the shape of a frustrum of a cone and equipped with screw conveyor flights in the annular space between it and the inner wall of the vertical cylinder. The pulp is fed-into the.

annular space and the inner member is rotated thus causing the screw conveyor flights to compress the pulp in the annular space as it passes downwardly therein, so that the water is squeezed out through the inner and outer perforations. Pulp passing out from the bottom of the annular space generally contains around 60% by weight of water and for the most part is in the form of some small agglomerates of fibers-e. gs

fibers. is essentially a solid material in divided form and can be handled mechanically like commonly known granular free-flowing materials, such as 7 seeds or sawdust. For want of a better term, We designate this as granular wood pulp. 7

As an illustration of the invention, the above into screw conveyor 2, which is rotated to feed the granular pulp into the rotating cylinder 3;

Aqueous peroxide bleaching solution is forced through pipe 5 and nozzles 6 to form a finely divided dispersion or mist of the solution in the air in cylinder 3. slow rate of speed commonly employed in rotary drier operations, so that the granular pulp is elevated by the lugs or baflles t to a point higher than the axis of the cylinder and thence dropped downward in a scattering manner.

a conventiona1 type capable of forming a finely described granular pulp is treated in the apparatus shown in the drawing. The granularpulp": is placed in hopper l whence it flows by gravity Cylinder 3 is rotated at the The granular pulp in cylinder 3 thus is repeatedly elevated solution from the mist-like dispersion. The granular pulp very rapidly absorbs the peroxide solution from ist so that the solution completely and uniformly impregnates each fiber and fiber agglomerate, thereby completel and uniformly impregnating the entire mass of granular pulp with the peroxide solution.

The concentration of peroxide in the bleach. ing solution may be varied over a Wide range,.

depending upon the desired extent of bleaching.

and the desired consistency of the pulp emerging from the rotating cylinder. Generally, it is preferred to utilize a sufliciently high concentration of peroxide so that the discharged pulp wilL still: have a high consistency, preferably not lower than about consistency, e. g., 20 to consistency. Other ingredients besides. hydrogen peroxide and alkali metal peroxides commonly utilized. in conventional peroxide bleach.-

ing solutions may be added in practicing this inperacids and their salts, e. g., perborates, peracetatm and the like.

The above preferred method of practicing the invention is given by way of example, and the invention is not necessarily restrictedthereto. In

its broader aspects, the invention comprises any method whereby wood pulp having a consistency of 30% or higher is brought into contact with a mist or similar finely divided dispersion of a peroxide solution. For example, the high consistency wood pulp may be spread'in a thin layer, as" on a conveyor; and thus brought into contact with the aforesaid dispersion or mist. For the best results and to obtain a complete and uniformdistribution of the bleaching-solution in the wood pulp, it is preferable that the latter be in a more or less finely divided state, such as the granular pulp described above. While such granular or finely divided pulp is most economicallyprepared'by means of a pulp press or-its-equivalent; such pulp also may be prepared by other means, for example, by shredding high consist ency pulp formed on a lapping machine,- or thelike. It is essential however that pul'pcontain notmore than 70% by'weight' of water, as at lower-consistencies the bleachingsolutionis not sufliciently rapidly absorbed from the mist to ob- We. prefer to. use

tain a complete and uniform distribution of the bleaching chemical within the'fiber clusters.- If desired, the pulp may be completely dewatered, i. e;, so that it contains little or nowater, but

there is no substantial advantage-in dewatering the pulp to a consistency of'more than about 50%; Itispreferrcd therefore to utilize pulp which-has been dewatered to a consistency of from 30 to about 50%.

It should be understood that statements here bleaching solution.

An advantage of the herein described invention iszthe: ease and rapidity with which the pulp is completely and uniforml impregnated with the bleaching agent. AI-urther advantage is the simplicity of control, resulting from the rapidity with which, the high consistency pulp absorbs bleaching solution from the peroxide mist. A further advantage is that the pulp, after impregnation withthebleaching solution may still have a high consistency such as 20 to 30% (i. e., a Water content of to by weight) and hence may be handled like a granular solid material.

We claim: v

1. The process for bleaching wood pulp which comprises forming a mist-like dispersion of arr alkaline aqueous peroxide solution in. air in an. enclosed space and passing through said. space in contact with said dispersion a substantially granular, free flowing, high consistency groundj woodpulp-initiallycontaining not less than about, 50%, and not more than 70% by weight of water, said gramilar-high consistency pulp being repeatedly elevatedand' scatteringly dropped during its passage through said space.

2. The process for bleaching Wood pulp which comprises forming a mist-like dispersion. of an aqueous" peroxide bleaching solution in air in an I enclosed space, forming a substantially granular, free-flowin high consistencywood pulp initially containing not less than about 50% and notmore than 70%" by weight of Water, introducing'said granular pulp into said space and therein mechanically acting on the pulp granulesto U scatter them through said mist-like dispersion and finally'removing said granules from said space.

3'. The process for bleaching wood pulp which comprises forming'a mist-like dispersion of an aqueous peroxide bleaching solution in air in' an enclosed space, forming a substantially granularfree flowlng high consistency wood pulp initially containlngnot' less than about'50"%' and not more than 70% by weight of water, introducin said granular pulp into-saidspaceand' therein repeat-- edly elevating and scatteringly dropping said granular-pulp through said mist-like dispersion until thepulp granules have absorbed suflicient ofsaid solution to contain 70 to 80% by weight" of'water andthen removing said granules from" said space;

PAUL B. K'BURG. JOSEPH Si REICHERT.

REFERENCES? GITED' The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date.

872,097 Buggenhoudt Nov. 26,19071' l 1,106,371 Donner Aug. 11; 1914. 1;409;799' Trostel Mar. 14, 19228; 1,529;919' Richter Mar. 17; 1925.; 1,795,757 Bradley Mar. 10, 19311 1=,9o7,54a' John May. 9'; 193a 1,968,994 Davies Aug; 7, 1934 2,194,358 Hundt' Mar. 19,.19'40:

Certificate of Correction Patent N 0. 2,492,047 December 20, 1949 PAUL B. KBURG ET AL.

It is hereby certified that errors appear in the above numbered patent requiring correction as follows:

In the grant, line 7, title of invention, for BLEACHING WOOD PULPS read BLEACHING WOOD PULP; column 4, list of references cited, add 2,465,788 McEwen "Mar. 29, 1.949;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 21st day of February, A. D. 1950.

THOMAS F. MURPHY,

Assistant O'Ommz'ssioner of Patents. 

